fix: Fix list comprehension variable names (NameError in CI)

Fixed incorrect variable names in list comprehensions that were causing
NameError in CI (Python 3.11/3.12):

Critical fixes:
- tests/test_markdown_parsing.py: 'l' → 'link' in list comprehension
- src/skill_seekers/cli/pdf_extractor_poc.py: 'l' → 'line' (2 occurrences)

Additional auto-lint fixes:
- Removed unused imports in llms_txt_downloader.py, llms_txt_parser.py
- Fixed comparison operators in config files
- Fixed list comprehension in other files

All tests now pass in CI.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/skill_seekers/cli/pdf_extractor_poc.py

@@ -299,7 +299,7 @@ class PDFExtractor:
         comment_lines = sum(
             1 for line in code.split("\n") if line.strip().startswith(("#", "//", "/*", "*", "--"))
         )
-        total_lines = len([l for line in code.split("\n") if line.strip()])
+        total_lines = len([line for line in code.split("\n") if line.strip()])
         if total_lines > 0 and comment_lines / total_lines > 0.7:
             issues.append("Mostly comments")
 
@@ -327,7 +327,7 @@ class PDFExtractor:
             score -= 2.0
 
         # Factor 3: Number of lines
-        lines = [l for line in code.split("\n") if line.strip()]
+        lines = [line for line in code.split("\n") if line.strip()]
         if 2 <= len(lines) <= 50:
             score += 1.0
         elif len(lines) > 100: